1. The Field of the Invention.
The present disclosure relates generally to an orthopedic prosthesis, and more particularly, but not necessarily entirely, to a prosthesis for implantation into a socket of a ball and socket joint of a human body.
2. Description of Related Art
The pelvis of a human generally comprises four major bones, namely two hip bones located on the front and lateral portions of the pelvis and the sacrum and the coccyx located behind the hip bones. The hip joint is formed essentially of portions of the hip bone and portions of the femur. Specifically, the hip bone is comprised of the ilium, the ischium, and the pubis, which are distinct portions in the human pelvis that start out in a person's youth as individual pieces of bone and become fused during a person's adulthood. Fusion of the ilium, the ischium, and the pubis occurs in and around the acetabulum, which is a substantially semispherical shaped, or substantially horse shoe shaped, articular cavity. The femur, which is the longest and strongest bone in the skeleton, comprises an upper and lower extremity as well as a body. The upper extremity comprises a femoral head, a femoral neck in addition to a greater and lesser trochanter. The femoral head articulates with the hip bone at the acetabulum, forming the ball and socket portions of the hip joint.
According to Henry Gray's classic text, Anatomy of the Human Body (1918), the movements of the hip are very extensive and comprise flexion, extension, adduction, abduction, circumduction, and rotation movements. Additionally, the hip plays an important role in weight bearing and permits a person to ambulate. Accordingly, the hip joint is subject to several various forces due to the complex movements listed above. Over time, degeneration of the hip joint is a relatively common problem that may manifest itself in various forms. Examples of such degeneration include, osteoarthritis (a process that directly results in the wearing out of cartilage on the joint surface), arthritis (a disease of the tissue that lines the inside of the joint, and results in the inflamation, stiffness and deformation of the joint), avascular necrosis (a disease where the blood supply to the femoral head of the joint is reduced), dislocation and fracture around the joint (may cause rapid degeneration of the joint), developmental dysplasia of the hip (a congenital deformity with symptoms ranging from a minor displacement of the femoral head out of the center of the acetabulum to a complete dislocation of the femoral head out of the acetabulum), as well as other anatomical deformities of the hip joint.
It is common practice for orthopedic surgeons to correct degenerative problems, or deformities of the hip joint by replacing the diseased, damaged, or otherwise compromised natural hip components with artificial prosthetic hip components. Over the years, manufacturers of prosthetic implants have attempted to imitate the biomechanics of the hip joint. More specifically, manufacturers of prosthetic implants have attempted to provide a bearing surface that may be implanted within the acetabulum with or without the need for a separate shell component, such that the implant substantially mirrors the functions of the natural articulation surfaces in the hip joint.
For example, U.S. Pat. No. 6,290,727 (granted Sep. 18, 2001 to Otto et al.) discloses an acetabular cup having an outer surface configured for resting in a cavity of the pelvis and an inner bearing surface configured for receiving a prosthetic head therein. The outer surface comprises a plurality of concentric annular grooves and a plurality of longitudinal grooves that are arranged transversely to said annular grooves exposing a plurality of surface segments therebetween. This design is disadvantageous because the surface segments formed by the grooves contain sharp edges and corners and are shaped in such a manner so as to create stress risers between the acetabular cup and the fixation material, which may cause cracking in the cement or other fixation material loosening the acetabular cup from the bone. Further, the grooves contain sidewalls that do not taper making it difficult for the cement or other fixation material to adhere to the acetabular cup.
Another example of a prosthetic implant having a bearing surface configured for direct implantation into the acetabulum is found in U.S. Pat. No. 5,549,701 (granted Aug. 27, 1996 to Mikhail). This patent discloses an acetabular cup member having an exterior surface with a plurality of annular grooves formed therein, and a plurality of grooves formed transversely to the annular grooves. The resulting configuration of the acetabular cup contains several raised segments that are sharp and have potential to cause stress risers, causing the acetabular cup to crack the surrounding cement or fixation material, thus loosening the acetabular cup from the bone. Similar to the '727 patent granted to Otto et al., the grooves of this patent lack a tapered sidewall and further lack an undercut surface that functions to enhance fixation, making it difficult to secure the acetabular cup within the bone. Therefore, this patent has several disadvantageous features that may be addressed by the present disclosure.
It is noteworthy that none of the prior art known to applicant provides a prosthetic implant capable of being directly implanted into a socket portion of a ball and socket joint that comprises a multi-directional and multi-planar recessed channel having rounded edges to decrease the occurrence of stress risers, and tapered walls that create an undercut surface for enhancing fixation between said implant and the bone cement or other fixation material. There is a long felt, but unmet need, for an acetabular cup that may be directly implanted into a socket, that is relatively inexpensive to make, simple in operation and that enhances fixation between the implant and the cement or other fixation materials to securely seat the implant within the socket.
The prior art is thus characterized by several disadvantages that are addressed by the present disclosure. The present disclosure minimizes, and in some aspects eliminates, the above-mentioned failures, and other problems, by utilizing the methods and structural features described herein.
The features and advantages of the disclosure will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by the practice of the disclosure without undue experimentation. The features and advantages of the disclosure may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims.